The overall objectives of these studies are to develop and evaluate techniques for obtaining quantitative measurements of the permeability characteristics of human dentin. Although most of the data collected will be from in vitro studies, similar studies done in dogs, both in vivo and in vitro will provide information about the validity of extrapolating in vitro observations in the in vivo situation. Attempts will be made to increase the permeability of dentin via iontophoresis, manipulation of solution osmolarity and the use of different solvents. Different methods of decreasing dentin permeability will also be evaluated. The permeability of dentin to a wide range of agents used in dentistry will be evaluated to determine the influence of molecular weight, molecular size, charge, and oil-water partition. Further studies will determine the hydraulic conductance of dentin. These will be based on the application of the indicator-dilution principle to measurement of micron 1 fluid shifts across dentin. The data collected will permit calculation of functional dentin tubular dimensions. The data collected from normal, sound dentin will be compared to data obtained from carious dentin.